I must admit, that I've never had many problems with killing him - but then again, I've never found any of the oppersition in NwN that difficult.
A few general suggestions I can make:
Use potions (or spells) to buff up you and your henchmen.
Haste is a valurable type of potion, unless you have boots of speed. Invisibility is also good to get a short break and rebuff. Barkskin, strenght, endurance and similar speaks for themselves - use them.
Also - don't rush to him, start by pulling all the extra creatures towards you (use missle weapons or similar) while keeping out of sight of Toras. It makes it loads easier to take him down if alone.
Stone of Recall. Use it, rest up/heal up, teleport back and repeat if he gives you problems.
Also - use a differnet henchmen if you find that the one you have in group dosen't perfom as good as he should. Daelan is good.
If you are a figther type, use Knockdown if you have it. You can keep a creature immobilized throughout a complete fight if you time your knockdowns correct. Knockdown each time he gets up.
Use items if you have them with abilities. You might have an item that could turn a fight, so check up on what you have.
If you are a spell caster, summons are good. Experiement with summons to find what suits you best against various types of enemies, in different fights.
Protection against death magic, fear and similar - or just plain magic resistance (Shimmering shash or something) are valurable against spellcasting enemies.
I hope some of these pointers will help you.
Otherwise post again, and we'll see if we can't get you past this NPC